An air-tight chamber of N-44 cu m capacity, made of 2 mm thick perspex sheets, fitted on a wooden frame, was fabricated to expose plants to air pollutnats, especially S02. The S02 gas was liberated inside the chamber by mixing concentrated sulphuric acid with moistened sodium sulphite. The S02-containing air of the chamber was bubbled through 0.1 n iodine solution to determine the resultant concentration of so2 inside the chamber. A number of minifans placed inside the chamber helped circulating air and preventions temprature rise Exposure of plants to gaseous ammonia may be possible, by allowing liquor ammonia to evaporate inside the chamber. The chamber was found suitable for exposing potted plants to gaseous pollutants under static conditions.

INTRODUCTION

Air pollution induced foliar injury to plants was noticed in the city of Bombay and it was felt necessary to compare the nature and extent of injury in the field with that produced after exposure to a given pollutant under laboratory conditions. For this purpose we attempted fabrication of a chamber on the model of Rao and Pal (1975), requiring moderate expenditure and limited laboratory space.

FABRICATION OF THE CHAMBER

The gas exposure chamber is an airtight 2 mm thick perspex cubicle of 5.44 cu m capacity, with a single door, mounted on a wooden platform. It is with four Philips 40 watt fluorescent tubes equivalent to daylight conditions for plants. The floor of the chamber is covered with a single sheet of thick plastic to make it airtight and to reduce the adsorption of gases on the rough, wooden surfaces. The chamber-top is fitted with an adjustable wooden shelf for inserting the stem of a separating funnel into the chamber. A minifan is placed opposite the shelf for proper mixing of the gas in the chamber. The exposure chamber is fitted with a leakproof glassstoppered outlet and an inlet. These are in use only when the chamber air is to be sucked out for analysis.

GENERATION OF SO2 IN THE CHAMBER AND ESTIMATION OF ITS CONCENTRTION

S02 is generated inside the chamber by mixing concentrated sulphuric acid with sodium sulphite by the following equation :

Quantities of sodium sulphite and sulphuric acid needed to produce a required concentration of gas in a chamber of known volume, were calculated Vogel 1961) and the required quantity of the salt is placed in a shallow watch glass and of the acid in the separating funnel. The door was closed and sealed airtight with a tape. By adjusting the funnel stopper sulphuric acid is allowed to mix with sodium sulphite in the watch glass placed on the shelf inside the chamber.Proper mixing of SO2 in the chamber is brought about by operating the minifan.

Reich's method as described by Dennis (1913) is employed for the estimation of S02 concentration inside the chamber, which is given by following reaction :


0.25 ml of 0 1 N iodine solution diluted to 40 ml distilled water was taken in a bubbler. 1 ml of 1% starch solution was added to it, to give the liquid an intense blue colour. An aspirator bottle was filled to capacity with tap water. Inlet tube of the bubbler was joined by a polythene tubing to the chamber outlet. The chamber and the aspirator outlets were opened and water was allowed to run out of the aspirator, until the gas started bubbling through the iodine solution. A measuring cylinder was placed at the end of the tube to collect water displaced from the aspirator. In this way, the gas was aspirated slowly through the iodine solution. The moment iodine solution got decolourised, the volume of water collected in the measuring cylinder was noted and the flow of air was stopped. The amount of air aspirated through the bubbler, corresponded to the water in the cylinder.

Since 1 ml of standard iodine solution 0.0032 gm SO2 1.18 cc of S02 at N. T. P., S02 concentration wascalculated by the given formula:


It was found that 7.6 gm of sodium sulphite plus 15 ml of water plus 14 ml of concentrated sulphuric acid (A. R. grade ) gave S02 concentration of 120.4 ppm. Concentrations upto l ppm S02 in the chamber were manipulated and estimated. For lower concentrations, the bubbler was connected to a suction pump instead of to the aspirator bottle and rate of bubbling was adjusted with a flowmeter at a convenient 3 lit / min. After fumigation, bubbling was started by operating the suction pump and time was noted. When the iodine solution decolourized, time was again noted and the on pump was stopped (Efremova et al., 1974). were done as before.

It was noted that the calculated actual concentration of SO2 in the chamber, varied very slightly from the estimated concentrations.

The variation was consistently within 10% or about 10% less concentration of S02 was obtained in all the tests. This may probably be due to the adsorption of the chamber walls.